1. Field of the Invention
The present invention generally relates to a power saving arrangement and power saving method for use in subsidiary unit, such as a handset unit, which communicates with a base unit in response to the detection of an ID signal produced from the base unit.
2. Description of the Prior Art
Recently, many developments have been made on pocket size receiver, for example, cordless telephones, radio pagers or portable telephones, which can effect wireless communication between a base unit and a handset unit.
In these receivers referred to above, portability is particularly emphasized, and accordingly a various circuit arrangements are incorporated in a monolithic IC or the like driven by a battery. Thus, from the viewpoint of power saving, a standby mode is presented. When the standby mode is established, the electric power from the battery is supplied to the various circuits intermittently in pulses having a predetermined frequency, so that the handset unit can detect and analyze the ID signal transmitted from the base unit. When the ID signal is detected, the handset unit is changed from the standby mode to the use mode to detect data signal following the ID signal, thereby starting communication between the handset unit and the base unit. Thus, during the standby mode, the power consumption is saved.
An example of a prior art power saving arrangement is shown in FIG. 4.
The circuit shown in FIG. 4 includes a battery 1 which is a power source for the handset unit such as in a cordless phone system, a radio frequency amplifier 2, a mixing circuit 3, a local oscillator 4, an intermediate frequency amplifier 5, a demodulator 6, a signal strength detecting circuit 7 which operates as a detector for detecting the signal level of the received signal, and a waveform shaping circuit 9 for shaping the ID signal from the demodulator 6. A CPU 10 functions to analyze the pattern of received ID signal and to change the mode between standby mode and use mode. During the standby mode, CPU 10 produces a power saving signal PSS to operation control circuit 11 which then produces power in pulses having a predetermined frequency, and supplies the pulsating power to various circuits. Such an intermittent power supply to various circuits is not sufficient to properly process the data signal from the base unit, but is sufficient to analyze the ID signal. Thus, during the standby mode, power necessary to analyze the ID signal is constantly supplied to the various circuits, such as to IF amplifier 5, demodulator 6 and waveshaping circuit 9. When the pattern of the detected ID signal coincides with the pattern stored in CPU 10, the mode is changed from the standby mode to use mode. Under the use mode, the power saving signal PSS is cut off so that the operation control circuit 11 continuously provides the full power to the various circuits.
According to the prior art power saving arrangement, since the intermediate frequency amplifier circuit 5, demodulator circuit 6 and waveform shaping circuit 9 are continuously operated even during the standby mode to analyze the ID signal, there is such a problem that the power consumption during the standby mode is still quite high.